Identification and localization of laminin chains in human retina

Purpose. Laminins are large heterotrimeric extracellular matrix proteins consisting of an α, a β, and a γ chain. We have shown that the β2 chain is one component of the extracellular matrix of the suhretinal space in adult and developing retinae and the β2 chain is likely to be involved in the development of rod photoreceptors in vitro and in vivo. Here, we extend our studies of laminins to address specifically the composition of laminin trimers in the human retina; this study will lay the foundation for an understanding of me role laminins may play in human disease. Methods. In situ hybridization was performed on paraffin sections of paraformaldehyde-fixed, adult retina using digoxigenin-Iabeled cRNA probes complementary to the following laminin chains: α1,2,3,4; β1,2,3; γ1,2. Indirect immunohistochemistry was performed on frozen sections of unfixed adult retina using antibodies directed against laminin trimers (laminin-1, α1/β1/γ1; laminin-5, α3\β3\γ2) or individual laminin chains (α2, α3, β2, β3, y2). Results. In situ hybridizations show that a number of laminin chains are expressed by cells, most probably Müller cells, in the INL. Strong signals were detected for a4 and β2, whereas <x3, β3, and y2 were expressed weakly. We did not detect al, cc2, βl, or yl RNA in the neural retina. Immunohistochemistry suggests that two of the laminin chains (ct3 and β2) are components of the IPM and surround inner segments; in addition, o3 and β2 are present in radial fibers spanning the retina. The distribution of ct3 and β2 suggests-as do the in situ hybridizations-that the Müller cell is a source of laminins in the adult retina. We have not detected al, a2, βl, β3,yl, ory2 protein in the neural retina. Conclusion. The vertebrate retina-in particular, the IPM-contains laminins that may serve as important molecules guiding photoreceptor development; in the adult, these laminins may participate in the maintenance of retinal adhesion and photoreceptor viability. Given that mutations in laminin chains cause human diseases, some with retinal involvement, it will be of interest to determine whether alterations in retinal laminin expression are involved in human pathologies.