The regulation of alpha-actinin-4 in podocytes and its role in focal segmental glomerulosclerosis

Title: The regulation of alpha-actinin-4 in podocytes and its role in focal segmental glomerulosclerosis
Authors: Hosseini-Abardeh, Mona
Date: 2007
Abstract: alpha-Actinin-4 is an actin crosslinking protein that supports the foot process architecture of the podocytes. Mutations in the ACTN4 gene underlie an autosomal dominant form of the glomerular lesion - Focal Segmental Glomerulosclerosis (FSGS). Affected individuals have a defective filtration barrier causing protein to leak into the urine. The K256E mutation dramatically increases alpha-actinin-4/actin affinity, alters alpha-actinin-4's intracellular localization in podocytes, and impairs cytoskeletal-dependent cell spreading and migration. Due to its mislocalization and enhanced affinity for F-actin, we hypothesized that the phosphorylation and interaction of K256E alpha-actinin-4 with its known binding partners would be disrupted. Furthermore, K256E alpha-actinin-4 would diminish the dynamic nature of the podocyte actin cytoskeleton upon exposure to mechanical stretch---a mimic of the in vivo intraglomerular capillary pressure. Tyrosine phosphorylation of alpha-actinin-4 could not be detected in cells overexpressing focal adhesion kinase (FAK) or in response to sodium orthovanadate---a tyrosine phosphatase inhibitor. Immunofluorescence, immunoprecipitation, and immunoblot approaches revealed that K256E alpha-actinin-4 exhibits reduced interaction with the adherens junction protein, beta-catenin, and affects distribution of the actin binding protein, synaptopodin, along stress fibers. Finally expression of K256E alpha-actinin-4 dramatically alters the morphology of podocytes, reducing the cytoplasmic surface area, in response to mechanical stretch. These findings demonstrate that the K256E alpha-actinin-4 is sequestered away from specific subcellular domains such that it cannot interact with some of its endogenous binding partners, while severely impacting the dynamic nature of the actin cytoskeleton. These perturbations may therefore underlie podocyte dysfunction in actinin-associated FSGS.
CollectionTh├Ęses, 1910 - 2010 // Theses, 1910 - 2010
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