[caption id="attachment_274" align="alignleft" width="298" caption="Mouse podocytes"]
[/caption] Organization of the actin cytoskeleton and focal adhesions in podocytes where dendrin (a transcription factor that promotes expression of cytosolic cathepsin L) has been downregulated. Focal adhesions and F-actin were visualized with antipaxillin (green) and rhodamine-phalloidin (red), respectively. Yaddanapudi and colleagues examine signaling pathways and molecular mechanisms that underlie proteinuric kidney disease.
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.
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