The Rho-GTPase binding protein IQGAP2 is required for the glomerular filtration barrier

Abstract

Podocyte dysfunction impairs the size selectivity of the glomerular filter, leading to proteinuria, hypoalbuminuria, and edema, clinically defined as nephrotic syndrome. Hereditary forms of nephrotic syndrome are linked to mutations in podocyte-specific genes. To identify genes contributing to podocyte dysfunction in acquired nephrotic syndrome, we studied human glomerular gene expression data sets for glomerular-enriched gene transcripts differentially regulated between pretransplant biopsy samples and biopsies from patients with nephrotic syndrome. Candidate genes were screened by in situ hybridization for expression in the zebrafish pronephros, an easy-to-use in vivo assay system to assess podocyte function. One glomerulus-enriched product was the Rho-GTPase binding protein, IQGAP2. Immunohistochemistry found a strong presence of IQGAP2 in normal human and zebrafish podocytes. In zebrafish larvae, morpholino-based knockdown of iqgap2 caused a mild foot process effacement of zebrafish podocytes and a cystic dilation of the urinary space of Bowman's capsule upon onset of urinary filtration. Moreover, the glomerulus of zebrafish morphants showed a glomerular permeability for injected high-molecular-weight dextrans, indicating an impaired size selectivity of the glomerular filter. Thus, IQGAP2 is a Rho-GTPase binding protein, highly abundant in human and zebrafish podocytes, which controls normal podocyte structure and function as evidenced in the zebrafish pronephros.

Weighted Gene Correlation Network Analysis (WGCNA) Detected Loss of MAGI2 Promotes Chronic Kidney Disease (CKD) by Podocyte Damage

“…Meanwhile, multiple genes in the green module have been reported to be involved directly in podocyte lesion, e.g. MME [53], CR1 [54], NPHS2 and IQGAP2 [55]. These results imply that genes in the green module may play important roles in multiple CKDs, particularly participating in podocyte damage.…”

Nucleoporin 133 deficiency leads to glomerular damage in zebrafish

“…Part of the albumin is endocytosed by the epithelial cells of the proximal tubules, while the rest gets then excreted via the final urine leading to proteinuria. In zebrafish larvae, it is possible to inject fluorescent compounds of specific size into the general circulation and then to monitor the appearance of fluorescent endosomes in the apical cytoplasm of pronephric tubule cells 33,34 . To assay for kidney function, we therefore injected fluorescently labeled albumin from Bovine Serum (BSA, Alexa Fluor™ 647 conjugate) into the common cardinal vein of wild type and nup133 morphant larvae at 4 dpf and then monitored the appearance of fluorescent endosomes in the cytoplasm of pronephric tubule cells.…”

Drug discovery in focal and segmental glomerulosclerosis

“…nephrin, PKCε and CD2AP knockout) lead to persistent proteinuria and glomerulosclerosis 42 . Similarly systems, such as those in the zebrafish, that can be used for screening suppressors or enhancers of a particular phenotype or in pharmacological screens 50 are also being increasingly used. However, because of availability, speed and cost, the PAN and LPS models appear to be the work horses of the community, although the models have a reversible phenotype and no efficacy/endpoint criteria that constitute a clinically meaningful effect have ever been formally recommended.…”