KANK deficiency leads to podocyte dysfunction and nephrotic syndrome
Heon Yung Gee, … , Zhe Han, Friedhelm Hildebrandt
Heon Yung Gee, … , Zhe Han, Friedhelm Hildebrandt
Published May 11, 2015
Citation Information: J Clin Invest. 2015;125(6):2375-2384. https://doi.org/10.1172/JCI79504.
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Research Article Nephrology

KANK deficiency leads to podocyte dysfunction and nephrotic syndrome

Abstract

Steroid-resistant nephrotic syndrome (SRNS) is a frequent cause of progressive renal function decline and affects millions of people. In a recent study, 30% of SRNS cases evaluated were the result of monogenic mutations in 1 of 27 different genes. Here, using homozygosity mapping and whole-exome sequencing, we identified recessive mutations in kidney ankyrin repeat-containing protein 1 (KANK1), KANK2, and KANK4 in individuals with nephrotic syndrome. In an independent functional genetic screen of Drosophila cardiac nephrocytes, which are equivalents of mammalian podocytes, we determined that the Drosophila KANK homolog (dKank) is essential for nephrocyte function. RNAi-mediated knockdown of dKank in nephrocytes disrupted slit diaphragm filtration structures and lacuna channel structures. In rats, KANK1, KANK2, and KANK4 all localized to podocytes in glomeruli, and KANK1 partially colocalized with synaptopodin. Knockdown of kank2 in zebrafish recapitulated a nephrotic syndrome phenotype, resulting in proteinuria and podocyte foot process effacement. In rat glomeruli and cultured human podocytes, KANK2 interacted with ARHGDIA, a known regulator of RHO GTPases in podocytes that is dysfunctional in some types of nephrotic syndrome. Knockdown of KANK2 in cultured podocytes increased active GTP-bound RHOA and decreased migration. Together, these data suggest that KANK family genes play evolutionarily conserved roles in podocyte function, likely through regulating RHO GTPase signaling.

Authors

Heon Yung Gee, Fujian Zhang, Shazia Ashraf, Stefan Kohl, Carolin E. Sadowski, Virginia Vega-Warner, Weibin Zhou, Svjetlana Lovric, Humphrey Fang, Margaret Nettleton, Jun-yi Zhu, Julia Hoefele, Lutz T. Weber, Ludmila Podracka, Andrej Boor, Henry Fehrenbach, Jeffrey W. Innis, Joseph Washburn, Shawn Levy, Richard P. Lifton, Edgar A. Otto, Zhe Han, Friedhelm Hildebrandt

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Figure 4

Functional analysis of kank2 knockdown in zebrafish.

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Functional analysis of kank2 knockdown in zebrafish. (A) Control zebrafi...
(A) Control zebrafish injected with p53 MO. p53 MO did not produce any phenotype until 168 hours after fertilization (n > 100). (B) Zebrafish coinjected with a MO targeting the translation initiation site of zebrafish kank2 (ATG MO) and p53 MO. At 120 hours after fertilization, kank2 morphants display the nephrosis phenotype of periorbital edema (arrows) and body edema in 54.5% of embryos (113 of 207). (C) Zebrafish coinjected with a MO targeting exon 2 splice donor site of kank2 (e2i2 MO) and p53 MO. e2i2 MO causes edematous phenotypes (arrows) in 52.3% of embryos (243 of 464). (D) Proteinuria assay in I-fabp::VDBP-GFP transgenic zebrafish. Note that knockdown of kank2 by either e2i2 or ATG MO causes significant proteinuria compared with that in control fish. (E and F) Electron microscopic structure of glomerular basement membrane and podocyte foot processes in 5-day-old (E) control and (F) kank2 morphant zebrafish. In the control, the foot processes are regularly spanned by slit diaphragms (arrows). In contrast, the foot processes of morphants are effaced and disorganized, with only occasional intercellular junctions (arrows in F). The glomerular basement membrane is disorganized. (G) Functional analysis of KANK2 mutations in zebrafish. Coinjection of kank2 e2i2 MO with a human wild-type KANK2 mRNA (156 of 491) partially rescued edematous phenotypes of kank2 morphants, whereas injection of KANK2 mRNA bearing the p.S181G (277 of 623) or p.S684F (187 of 447) mutation failed to rescue the phenotype. Error bars indicate the SD of more than 3 independent experiments. *P < 0.05, 2-tailed Student’s t test. Scale bar: 1 mm (A–C); 1 μm (E and F).