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      Laminin Heterogeneity around Schlemm’s Canal in Normal Humans and Glaucoma Patients

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          Background: The laminins play an important role in cell attachment to the extracellular matrix. This study was undertaken in order to investigate and to compare the presence of several laminin chains and isoforms in normal and glaucomatous trabecular meshwork. Methods: Fresh-frozen trabeculectomy specimens from glaucoma patients and trabecular meshwork from human donor eyes were included for immunohistochemistry. We used antibodies against laminin 1 (EHS-laminin/α1β1γ1), laminin 2 (merosin/α2β1γ1), the subunits α2 (M laminin), β1 (B1 laminin), γ1 (B2 laminin), β2 (s laminin) and γ2 and the laminin-associated glycoprotein nidogen. Results: For laminin 1, laminin 2, the subunits α2, β1, β2, γ1 and nidogen, the immunoreactivity of the juxtacanalicular zone underneath the inner wall of Schlemm’s canal was always stronger than of the uveal and corneoscleral trabecular meshwork. Staining for laminin chain γ2 could not be demonstrated in the outflow structures. Pattern and intensity of labelling for the laminins were not different between normal and glaucomatous eyes. Discussion: Heterogeneity of the laminins suggests structural complexity of the juxtacanalicular region. However, the presence of laminin around Schlemm’s canal seems to be unaffected by glaucoma and by age. This might indicate maintenance of basement membrane stability in the trabecular meshwork for life.

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          The Laminin α Chains: Expression, Developmental Transitions, and Chromosomal Locations of α1-5, Identification of Heterotrimeric Laminins 8–11, and Cloning of a Novel α3 Isoform

          Laminin trimers composed of α, β, and γ chains are major components of basal laminae (BLs) throughout the body. To date, three α chains (α1–3) have been shown to assemble into at least seven heterotrimers (called laminins 1–7). Genes encoding two additional α chains (α4 and α5) have been cloned, but little is known about their expression, and their protein products have not been identified. Here we generated antisera to recombinant α4 and α5 and used them to identify authentic proteins in tissue extracts. Immunoprecipitation and immunoblotting showed that α4 and α5 assemble into four novel laminin heterotrimers (laminins 8–11: α4β1γ1, α4β2γ1, α5β1γ1, and α5β2γ1, respectively). Using a panel of nucleotide and antibody probes, we surveyed the expression of α1-5 in murine tissues. All five chains were expressed in both embryos and adults, but each was distributed in a distinct pattern at both RNA and protein levels. Overall, α4 and α5 exhibited the broadest patterns of expression, while expression of α1 was the most restricted. Immunohistochemical analysis of kidney, lung, and heart showed that the α chains were confined to extracellular matrix and, with few exceptions, to BLs. All developing and adult BLs examined contained at least one α chain, all α chains were present in multiple BLs, and some BLs contained two or three α chains. Detailed analysis of developing kidney revealed that some individual BLs, including those of the tubule and glomerulus, changed in laminin chain composition as they matured, expressing up to three different α chains and two different β chains in an elaborate and dynamic progression. Interspecific backcross mapping of the five α chain genes revealed that they are distributed on four mouse chromosomes. Finally, we identified a novel full-length α3 isoform encoded by the Lama3 gene, which was previously believed to encode only truncated chains. Together, these results reveal remarkable diversity in BL composition and complexity in BL development.
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            A new nomenclature for the laminins.

            The authors have adopted a new nomenclature for the laminins. They are numbered with arabic numerals in the order discovered. The previous A, B1 and B2 chains, and their isoforms, are alpha, beta and gamma, respectively, followed by an arabic numeral to identify the isoform. For example, the first laminin identified from the Engelbreth-Holm-Swarm tumor is laminin-1 with the chain composition alpha 1 beta 1 gamma 1. The genes for these chains are LAMA1, LAMB1 and LAMC1, respectively.

              Author and article information

              Ophthalmic Res
              Ophthalmic Research
              S. Karger AG
              December 1998
              05 October 1998
              : 30
              : 6
              : 380-387
              Departments of a Ophthalmology and b Biochemistry, Medical Faculty, University of Cologne, Germany
              55499 Ophthalmic Res 1998;30:380–387
              © 1998 S. Karger AG, Basel

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              Page count
              Figures: 6, Tables: 1, References: 26, Pages: 8
              Original Paper


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