Apoptosis in podocytes induced by TGF-β and Smad7
Mario Schiffer, … , Peter Mundel, Erwin P. Böttinger
Mario Schiffer, … , Peter Mundel, Erwin P. Böttinger
Published September 15, 2001
Citation Information: J Clin Invest. 2001;108(6):807-816. https://doi.org/10.1172/JCI12367.
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Article

Apoptosis in podocytes induced by TGF-β and Smad7

Abstract

Primary and secondary forms of focal segmental glomerulosclerosis (FSGS) are characterized by depletion of podocytes and constitute a central manifestation of chronic progressive glomerular diseases. Here we report that podocytes undergo apoptosis at early stages in the course of progressive glomerulosclerosis in TGF-β1 transgenic mice. Apoptosis is associated with progressive depletion of podocytes and precedes mesangial expansion. Smad7 protein expression is strongly induced specifically in damaged podocytes of transgenic mice and in cultured murine podocytes treated with TGF-β. TGF-β1 and Smad7 each induce apoptosis in podocytes, and their coexpression has an additive effect. Activation of p38 MAP kinase and caspase-3 is required for TGF-β–mediated apoptosis, but not for apoptosis induced by Smad7. Unlike TGF-β, Smad7 inhibits nuclear translocation and transcriptional activity of the cell survival factor NF-κB. Our results suggest a novel functional role for Smad7 as amplifier of TGF-β−induced apoptosis in podocytes and a new pathomechanism for podocyte depletion in progressive glomerulosclerosis.

Authors

Mario Schiffer, Markus Bitzer, Ian S.D. Roberts, Jeffrey B. Kopp, Peter ten Dijke, Peter Mundel, Erwin P. Böttinger

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Figure 5

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(a) Western blot demonstrates levels of Flag-Smad7 in podocytes maintain...
(a) Western blot demonstrates levels of Flag-Smad7 in podocytes maintained under permissive conditions. Adenoviral vectors containing either control LacZ or Flag-Smad7 cDNAs were used to infect cells at various moi’s, as indicated. (b) Histogram shows the normalized average numbers of apoptotic cells visualized by DAPI per hpf (in 50 hpf total) from a representative experiment. Podocyte cultures were infected with AdLacZ or AdSmad7 adenoviral vectors and left untreated or treated with TGF-β1 in the absence or presence of caspase-3 inhibitor zVAD-fmk. Results were normalized for cell density. (c) Relative enzymatic activity of caspase-3 measured as fluorochrome release at 460 nm in infected podocytes cultured under permissive conditions in the absence (–) or presence (+) of TGF-β1. Enzyme activity is normalized to uninfected podocytes (set at 1). (d) Histogram shows the normalized average numbers of apoptotic cells as detected by TUNEL assay per hpf (in 50 hpf total) from a representative experiment. Podocyte cultures were infected with AdLacZ or AdSmad7 adenoviral vectors and left untreated or treated with TGF-β in the presence of control mouse immunoglobulin (IgG) or panneutralizing anti–TGF-β1 antibody (2G7). Results were normalized for total cell density.