Role of dynamin, synaptojanin, and endophilin in podocyte foot processes
Keita Soda, … , Pietro De Camilli, Shuta Ishibe
Keita Soda, … , Pietro De Camilli, Shuta Ishibe
Published November 26, 2012
Citation Information: J Clin Invest. 2012;122(12):4401-4411. https://doi.org/10.1172/JCI65289.
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Research Article

Role of dynamin, synaptojanin, and endophilin in podocyte foot processes

Abstract

Podocytes are specialized cells that play an integral role in the renal glomerular filtration barrier via their foot processes. The foot processes form a highly organized structure, the disruption of which causes nephrotic syndrome. Interestingly, several similarities have been observed between mechanisms that govern podocyte organization and mechanisms that mediate neuronal synapse development. Dynamin, synaptojanin, and endophilin are functional partners in synaptic vesicle recycling via interconnected actions in clathrin-mediated endocytosis and actin dynamics in neurons. A role of dynamin in the maintenance of the kidney filtration barrier via an action on the actin cytoskeleton of podocytes was suggested. Here we used a conditional double-KO of dynamin 1 (Dnm1) and Dnm2 in mouse podocytes to confirm dynamin’s role in podocyte foot process maintenance. In addition, we demonstrated that while synaptojanin 1 (Synj1) KO mice and endophilin 1 (Sh3gl2), endophilin 2 (Sh3gl1), and endophilin 3 (Sh3gl3) triple-KO mice had grossly normal embryonic development, these mutants failed to establish a normal filtration barrier and exhibited severe proteinuria due to abnormal podocyte foot process formation. These results strongly implicate a protein network that functions at the interface between endocytosis and actin at neuronal synapses in the formation and maintenance of the kidney glomerular filtration barrier.

Authors

Keita Soda, Daniel M. Balkin, Shawn M. Ferguson, Summer Paradise, Ira Milosevic, Silvia Giovedi, Laura Volpicelli-Daley, Xuefei Tian, Yumei Wu, Hong Ma, Sung Hyun Son, Rena Zheng, Gilbert Moeckel, Ottavio Cremona, Lawrence B. Holzman, Pietro De Camilli, Shuta Ishibe

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Figure 3

Lack of Synj1 results in severe proteinuria and foot process effacement.

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Lack of Synj1 results in severe proteinuria and foot process effacement....
(A) Western blots of total homogenates of brain and purified podocytes of neonatal control and Synj1 KO mice, demonstrating that podocytes selectively expressed Synj1-170, not Synj1-145. β-Actin served as a loading control. (B) Synj1 immunofluorescence staining of isolated primary podocytes and kidney sections of control and Synj1 KO mice. Scale bars: 10 μm (top); 30 μm (bottom). (C) Immunofluorescence for Synj1 and for the podocyte nuclear marker WT1 on an isolated podocyte. Scale bar: 20 μm. (D) Colocalization of Synj1 and clathrin heavy chain (CHC) in cultured podocytes. Scale bar: 20 μm. (E) Colocalization of Synj1 and nephrin in the glomerulus. Scale bar: 20 μm. (F) SDS-PAGE (Coomassie Blue stain) of 0.5, 1, or 10 μg BSA standard and of urine (2 μl) from control and Synj1 KO neonatal mice. (G) Quantification of urinary albumin normalized to creatinine (n = 12). *P < 0.001 vs. control. (H) Electron micrographs from glomeruli of control and Synj1 KO neonatal mice revealing foot process effacement and clathrin-coated intermediates in Synj1 KO mice. Boxed regions illustrate effaced podocytes in Synj1 KO mice compared with control. Scale bars: 500 nm.