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Title

Genetic and Molecular Analyses of Laminin-521 in the Kidney Glomerular Basement Membrane

Date of Award

Summer 8-15-2012

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Molecular Genetics & Genomics)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Laminin-521 (α5β2γ1) is the major laminin isoform in the mature kidney glomerular basement membrane (GBM), which, together with slit diaphragms of glomerular epithelial cells (podocytes) and fenestrated glomerular endothelial cells, helps establish the glomerular filtration barrier by preventing the leakage of plasma proteins. Mutations in laminin β2, in both human and mouse, lead to nephrotic syndrome with heavy proteinuria, indicating the essential role of laminin-521 in the glomerular filtration barrier. From the observation that laminin β1, a structural homolog of laminin β2, is marginally increased in the GBM in both humans and mice lacking laminin β2, we hypothesized that an increase of laminin β1 expression in podocytes would rescue the nephrotic syndrome in laminin β2 mutant mice. Podocyte-specific laminin β1 expression in laminin β2 mutant mice via a transgene indeed prevented the development of nephrotic syndrome and contributed to increased lifespan by establishing a structurally and functionally similar laminin-511 (α5β1γ1) network in the GBM. These results suggest that upregulation of laminin β1 in podocytes will attenuate nephrotic syndrome in patients carrying laminin β2 mutations.

Laminin-521 trimers are secreted by both podocytes and glomerular endothelial cells and self-polymerize into a supramolecular network that is essential for formation of the GBM. To investigate the dynamics of laminin-521 in the GBM, I utilized chimeric and transgenic mouse models to cause secretion of a labeled, immunologically distinct laminin-521 from a fraction of podocytes. By immunofluorescence analysis of the different mouse models, I have traced the labeled laminin-521 and found that laminin-521 diffused in the GBM, but in a limited fashion. Most of secreted laminin-521 trimers were found in the GBM close to the site of secretion, and some of them traveled about 10 μm on average within the GBM. These results suggest that secreted free laminins are quickly sequestered into the adjacent laminin network, and only a subset of free laminins can diffuse a far distance. These results have implications for glomerular diseases with deposition of ectopic laminins that may contribute to glomerular filtration barrier defects.

Language

English (en)

Chair and Committee

Jeffrey H Miner

Committee Members

Feng Chen, Robert P Mecham, Robert M Senior, Andrey S Shaw, Susan K Dutcher

Comments

Permanent URL: https://doi.org/10.7936/K7J96498

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