Actin Filament Organization of Foot Processes in Rat Podocytes

Abstract

S U M M A R YThe foot processes of podocytes possess abundant microfilaments and modulate glomerular filtration. We investigated the actin filament organization of foot processes in adult rat podocytes and the formation of the actin cytoskeletal system of immature podocytes during glomerulogenesis. Electron microscopy revealed two populations of actin cytoskeletons in foot processes of adult podocytes. One is the actin bundle running above the level of slit diaphragms and the other is the cortical actin network located beneath the plasmalemma. Immunogold labeling for actin-binding proteins demonstrated that ␣ -actinin and synaptopodin were localized in the actin bundle, whereas cortactin was in the cortical actin network. Immunofluorescence labeling for actin-binding proteins in immature podocyte showed that ␣ -actinin was localized at the level of the junctional complex, whereas cortactin was distributed beneath the entire plasmalemma. Synaptopodin was first observed along the basal plasmalemma from the advanced S-shaped body to the capillary loop stage. We conclude that foot processes have specialized actin filamentous organization and that its establishment is associated with the expression and redistribution of actin-binding proteins during development.

Permselective Dysfunction of Podocyte-Podocyte Contact upon Angiotensin II Unravels the Molecular Target for Renoprotective Intervention

“…In this cell line, we have shown that actin-associated ZO-1 is redistributed in response to Ang II, as are ␣-and ␤-catenin and ␣-actinin, which colocalize with ZO-1 in the foot process. 10,23 Paracellular permeability assays performed in a murine podocyte line by using anionic dextran (3 to 70 kd) have recently documented that podocytes establish a size-selective barrier dependent on differentiation. 40 One key finding here is that the altered ZO-1 distribution in differentiated mouse podocytes exposed to Ang II was paralleled by increased albumin permeabil- ity across the monolayer.…”

“…[3][4][5] Besides location at or near the intercellular contact, these molecules share interactions with each other and the actin cytoskeleton. 6 -8 The latter is increasingly thought to play a central role in maintaining podocyte structure and function 3,9,10 and to contribute to reorganization of the foot process in proteinuric nephropathies. 11,12 One pivotal mediator of progressive renal injury, angiotensin II (Ang II), may play a direct role in the pathogenesis of proteinuria.…”

MAGI-1 is a component of the glomerular slit diaphragm that is tightly associated with nephrin

“…36 Briefly, rat kidneys were perfused with 2% paraformaldehyde fixative buffered with 0.1 M phosphate buffer (PB, pH 7.4). These samples were immersed in the same fixative for about 30 min.…”

.BETA.-Cytoplasmic actin localization in vertebrate glomerular podocytes

“…SDS-PAGE and immunoblot analyses were performed as described previously (Ichimura et al, 2003). In brief, 2007).…”

“…In vertebrates, the major cytoskeletal component in the foot processes is actin filaments, which are organized into three kinds of actin cytoskeletons in the processes (Andrews and Bates, 1984;Vasmant et al, 1984;Drenckhahn and Franke, 1988;Ichimura et al, 2003, Summary.The unique cytoarchitecture of glomerular podocytes is conserved in vertebrate evolution. Actin filaments play a crucial role in the formation of the conserved cytoarchitecture, though several isoforms of cytoplasmic actin have been found in vertebrates.…”