Cytoskeleton-associated protein 4 affects podocyte cytoskeleton dynamics in diabetic kidney disease
Roberto Boi, Emelie Lassén, Alva Johansson, Peidi Liu, Aditi Chaudhari, Ramesh Tati, Janina Müller-Deile, Mario Schiffer, Kerstin Ebefors, Jenny Nyström
Roberto Boi, Emelie Lassén, Alva Johansson, Peidi Liu, Aditi Chaudhari, Ramesh Tati, Janina Müller-Deile, Mario Schiffer, Kerstin Ebefors, Jenny Nyström
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Research Article Cell biology Nephrology

Cytoskeleton-associated protein 4 affects podocyte cytoskeleton dynamics in diabetic kidney disease

Abstract

Podocytes are kidney glomerular cells that depend on rigorously regulated cytoskeleton components and integrins to form and maintain the so-called foot processes, apparatuses that attach podocytes to the glomerular basement membrane and connect them to neighboring podocytes. In diabetic kidney disease (DKD) these foot processes are effaced as a result of cytoskeleton dysregulation, a phenomenon that gradually reduces glomerular filtration. Cytoskeleton-associated protein 4 (CKAP4) is a known linker between the endoplasmic reticulum, integrins, and microtubular cytoskeleton. Since CKAP4 gene expression is downregulated in glomeruli from patients with DKD but not in other chronic kidney diseases, we hypothesized a role for CKAP4 in the mechanisms leading to foot process effacement (FPE) in DKD. CKAP4 mRNA reduction in podocytes in DKD was demonstrated in human kidney biopsies. Knockdown of CKAP4 in vivo in zebrafish resulted in edema, proteinuria, and foot process effacement, all typical features of DKD. Knockdown of CKAP4 in vitro led to disruption of the actin cytoskeleton and of the microtubular orientation. Moreover, it caused a downregulation of several integrins. These findings indicate that CKAP4 is crucial for foot process dynamics of podocytes. Its reduction, unique to DKD, is mechanistically connected to the pathophysiological processes leading to podocyte FPE.

Authors

Roberto Boi, Emelie Lassén, Alva Johansson, Peidi Liu, Aditi Chaudhari, Ramesh Tati, Janina Müller-Deile, Mario Schiffer, Kerstin Ebefors, Jenny Nyström

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Figure 7

CKAP4 KD influences protein families related to cytoskeleton dynamics.

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CKAP4 KD influences protein families related to cytoskeleton dynamics. V...
Volcano plot of selected proteins from the proteomic analysis of CKAP4 KD versus scr-treated HPODs. Dotted lines represent the P-adjusted threshold of 0.05 (y axis) and fold-change thresholds of ±20% (x axis). Protein variations within these lines were considered not significant and/or not regulated (A). The diagram on the upper right side illustrates the dysregulation of ACT (actins), MT (microtubules), and ITG (integrins). Key proteins have modulatory or structural functions in between these groups: RAP1 (ACT and ITG), DST (dystonin; ATC, and MT), and TLN1 (talin 1; ITG and ACT). Heatmap of selected proteins from the proteomics analysis. The color pattern legend identifies protein families in A and B. The P-adjusted filter was set at 0.05, and proteins were sorted by increasing fold-change. The color scale ranging from red to blue indicates degrees of upregulation (red) and downregulation (blue) or no regulation (white) (B). Heatmap of all the integrins detected in CKAP4 KD, scr-treated, and untreated cells (C). Protein lists are given in Table 3. Integrins are ranked by increasing fold-change (KD vs. scrambled). The q value scale ranges from blue (NS) to red (<0.05). No q value threshold was imposed. Confirmation of the expression of microtubule modulators MAP1A and DST in CKAP4 KD HPODs with Western blot (D). Total protein blots and normalized protein expression graphs are also presented. D: n = 4 per group, Tukey’s post hoc after 1-way ANOVA. *P < 0.05, **P < 0.01, ***P < 0.001. Error bars represent average ± SEM. AU, arbitrary units; CKAP4, cytoskeleton associated protein 4; KD, knockdown; scr, scrambled; ITGA6, integrin α6; MAP1A, microtubule associated protein 1A; DST, dystonin.