Shigatoxin-Induced Endothelin-1 Expression in Cultured Podocytes Autocrinally Mediates Actin Remodeling

Abstract

Shigatoxin (Stx) is the offending agent of post-diarrheal hemolytic uremic syndrome, characterized by glomerular ischemic changes preceding microvascular thrombosis. Because podocytes are highly sensitive to Stx cytotoxicity and represent a source of vasoactive molecules, we studied whether Stx-2 modulated the production of endothelin-1 (ET-1), taken as candidate mediator of podocyte dysfunction. Stx-2 enhanced ET-1 mRNA and protein expression via activation of nuclear factor B (NF-B) and activator protein-1 (Ap-1) to the extent that transfection with the dominant-negative mutant of IB-kinase 2 or with Ap-1 decoy oligodeoxynucleotides reduced ET-1 mRNA levels. We propose a role for p38 and p42/44 mitogen-activated protein kinases (MAPKs) in mediating NF-B-dependent gene transcription induced by Stx-2, based on data that Stx-2 phosphorylated p38 and p42/44 MAPKs and that MAPK inhibitors reduced transcription of NF-B promoter/luciferase reporter gene construct induced by Stx-2. Stx-2 caused F-actin redistribution and intercellular gaps via production of ET-1 acting on ET A receptor, because cytoskeleton changes were prevented by ET A receptor blockade. Exogenous ET-1 induced cytoskeleton rearrangement and intercellular gaps via phosphatidylinositol-3 kinase and Rho-kinase pathway and increased protein permeability across the podocyte monolayer. These data suggest that the podocyte is a target of Stx, a novel stimulus for the synthesis of ET-1, which may control cytoskeleton remodeling and glomerular permeability in an autocrine fashion.

The Vascular Endothelial Growth Factor Receptor Inhibitor Sunitinib Causes a Preeclampsia-Like Syndrome With Activation of the Endothelin System

“…This effect is BP independent and is mediated by a direct effect on the cytoskeleton of podocytes. 27,28 Thus, the observed decrease in proteinuria with macitentan might be a direct consequence of renal ET receptor blockade. In addition, BP decreased by 60% during administration of macitentan.…”

(Na+ + K+)-ATPase Is a Target for Phosphoinositide 3-Kinase/Protein Kinase B and Protein Kinase C Pathways Triggered by Albumin

“…In a previous work, we showed that only albumin concentrations of 10 -20 mg/ml induce apoptosis in LLC-PK1 cells (8). Then, even though the GSC for albumin is higher than has been proposed, the albumin concentration in the lumen of the PT does not reach the concentration that causes toxic effects on these cells (17,(21)(22)(23). In the present work, we showed that albumin concentrations ranging from 0.001 up to 1.0 mg/ml increased (Na ϩ ϩ K ϩ )-ATPase activity.…”

“…It was shown that cellular responses such as activation of PKB, JAK/STAT, NF-B, and MAPK pathways are triggered by interaction between albumin and megalin (8,17,(22)(23)(24). In the present work, we showed that PI3K/PKB activation is involved in the effect of lower albumin concentrations on PT (Na ϩ ϩ K ϩ )-ATPase activity.…”

Insulin-Like Growth Factor-1 Sustains Stem Cell–Mediated Renal Repair

“…RT-PCR and quantitative RT-PCR were performed as described previously. 50,51 Primer sequences are shown in Table 1.…”