Alterations of podocytes in a murine model of crescentic glomerulonephritis

Abstract

Recent observations suggest a central role of podocytes in crescent formation. In experimental glomerulonephritis podocytes disrupt the parietal epithelial layer and attach on its basement membrane, thus forming bridges between the tuft and Bowman's capsule, and they are a major constituent of crescents. In order to explain these findings we hypothesize that inflammation triggers motility in podocytes. In the present study we asked whether podocytes display alterations which suggest a migratory behavior in glomerulonephritis. Glomerulonephritis was induced in mice by injection of a rabbit serum against the glomerular basement membrane. The kidneys were perfusion-fixed 6 days later and examined by light and electron microscopy as well as by immunohistochemistry. In glomerulonephritis the apical cytoplasm of podocytes displayed numerous actin-containing microprotrusions. Cortactin, a protein involved in the regulation of actin polymerization, was predominantly expressed in foot processes of podocytes in control mice. It was redistributed to the cell body in glomerulonephritis. In untreated mice betal-integrin was restricted to the foot processes. In glomerulonephritis it was additionally found in the cytoplasm and in the apical cell membrane. Recycling of integrins is a crucial event in initiation of cell migration. ICAM-1 and CD44, the ligation of which induces migratory behaviors, were absent from healthy podocytes but expressed by some podocytes in glomerulonephritis. Thus, in glomerulonephritis podocytes display some characteristic features of migrating cells. This might explain their ability to break through the parietal epithelium and to become a constituent of early crescents.

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“…CD44 is a glycoprotein involved in cell adhesion, cell matrix interaction, and cell migration (17,18). Its expression by activated PECs points to a role for this adhesion molecule in the guided migration of PECs onto the glomerular tuft to replace injured/lost podocytes (16,19).…”

Nuclear Factor Erythroid 2-Related Factor 2 Drives Podocyte-Specific Expression of Peroxisome Proliferator-Activated Receptor γ Essential for Resistance to Crescentic GN

“…[1][2][3] Recent data have confirmed that podocytes also contribute to crescent formation in man, 4,5 although there is a great deal of heterogeneity in those affected, suggesting that in some cases local regulatory mechanisms fail to maintain a quiescent podocyte phenotype. Hence, modulation of podocyte phenotype may help the glomerulus to withstand inflammatory stress and to prevent, or arrest, the destructive process of crescent formation.…”