CD2AP in mouse and human podocytes controls a proteolytic program that regulates cytoskeletal structure and cellular survival
Suma Yaddanapudi, … , Sanja Sever, Jochen Reiser
Suma Yaddanapudi, … , Sanja Sever, Jochen Reiser
Published September 12, 2011
Citation Information: J Clin Invest. 2011;121(10):3965-3980. https://doi.org/10.1172/JCI58552.
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Research Article Nephrology

CD2AP in mouse and human podocytes controls a proteolytic program that regulates cytoskeletal structure and cellular survival

Abstract

Kidney podocytes are highly differentiated epithelial cells that form interdigitating foot processes with bridging slit diaphragms (SDs) that regulate renal ultrafiltration. Podocyte injury results in proteinuric kidney disease, and genetic deletion of SD-associated CD2-associated protein (CD2AP) leads to progressive renal failure in mice and humans. Here, we have shown that CD2AP regulates the TGF-β1–dependent translocation of dendrin from the SD to the nucleus. Nuclear dendrin acted as a transcription factor to promote expression of cytosolic cathepsin L (CatL). CatL proteolyzed the regulatory GTPase dynamin and the actin-associated adapter synaptopodin, leading to a reorganization of the podocyte microfilament system and consequent proteinuria. CD2AP itself was proteolyzed by CatL, promoting sustained expression of the protease during podocyte injury, and in turn increasing the apoptotic susceptibility of podocytes to TGF-β1. Our study identifies CD2AP as the gatekeeper of the podocyte TGF-β response through its regulation of CatL expression and defines a molecular mechanism underlying proteinuric kidney disease.

Authors

Suma Yaddanapudi, Mehmet M. Altintas, Andreas D. Kistler, Isabel Fernandez, Clemens C. Möller, Changli Wei, Vasil Peev, Jan B. Flesche, Anna-Lena Forst, Jing Li, Jaakko Patrakka, Zhijie Xiao, Florian Grahammer, Mario Schiffer, Tobias Lohmüller, Thomas Reinheckel, Changkyu Gu, Tobias B. Huber, Wenjun Ju, Markus Bitzer, Maria P. Rastaldi, Phillip Ruiz, Karl Tryggvason, Andrey S. Shaw, Christian Faul, Sanja Sever, Jochen Reiser

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Figure 2

Prolonged loss of CD2AP leads to expression of cytosolic CatL.

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Prolonged loss of CD2AP leads to expression of cytosolic CatL. (A) Actin...
(A) Actin cytoskeleton and FA organization in fully differentiated low- and high-Tgfb1Cd2ap–/– cells. Note the loss of well-defined stress fibers and dramatic increase in number of transverse arcs in high-Tgfb1Cd2ap–/– cells. FAs and F-actin were visualized with anti-paxillin antibodies and rhodamine-phalloidin, respectively. (B) Low-Tgfb1Cd2ap–/– podocytes could be transformed into high-Tgfb1Cd2ap–/– podocytes by high TGF-β1 levels. WT and low-Tgfb1Cd2ap–/– passage cells were treated with 5 ng/ml TGF-β1 in the media for 24 hours. Actin cytoskeleton was monitored by staining cells with rhodamine-phalloidin, and dendrin localization was monitored using anti-dendrin antibody (green). (C–E) mRNA levels for Tgfb1 (C) and Ctsl (D and E), determined by RT-PCR in podocytes. When indicated, cells were treated with 5 ng/ml TGF-β1 for 24 hours or with 50 μM LPS for 24 hours. Podocytes expressing Actn4 mutant are also shown in E. (F) Subcellular fractionation of low- and high-Tgfb1Cd2ap–/– podocytes in isotonic sucrose. Total proteins from soluble (S) and particulate (P) fractions were probed for CatL and for the lysosomal protein markers Lamp-2 and mannosidase (Manno), then analyzed by Western blotting. GAPDH was used as a loading control. Strong cytosolic CatL induction (asterisk) was observed in both soluble and pellet fractions of high-Tgfb1Cd2ap–/– podocytes. Scale bars: 20 μm.