Dysregulated Dynein-Mediated Trafficking of Nephrin Causes INF2-related Podocytopathy

Abstract

Background FSGS caused by mutations in INF2 is characterized by a podocytopathy with mistrafficked nephrin, an essential component of the slit diaphragm. Because INF2 is a formin-type actin nucleator, research has focused on its actin-regulating function, providing an important but incomplete insight into how these mutations lead to podocytopathy. A yeast two-hybridization screen identified the interaction between INF2 and the dynein transport complex, suggesting a newly recognized role of INF2 in regulating dynein-mediated vesicular trafficking in podocytes. Methods Live cell and quantitative imaging, fluorescent and surface biotinylation-based trafficking assays in cultured podocytes, and a new puromycin aminoglycoside nephropathy model of INF2 transgenic mice were used to demonstrate altered dynein-mediated trafficking of nephrin in INF2 associated podocytopathy. Results Pathogenic INF2 mutations disrupt an interaction of INF2 with dynein light chain 1, a key dynein component. The best-studied mutation, R218Q, diverts dynein-mediated postendocytic sorting of nephrin from recycling endosomes to lysosomes for degradation. Antagonizing dynein-mediated transport can rescue this effect. Augmented dynein-mediated trafficking and degradation of nephrin underlies puromycin aminoglycoside-induced podocytopathy and FSGS in vivo. Conclusions INF2 mutations enhance dynein-mediated trafficking of nephrin to proteolytic pathways, diminishing its recycling required for maintaining slit diaphragm integrity. The recognition that dysregulated dynein-mediated transport of nephrin in R218Q knockin podocytes opens an avenue for developing targeted therapy for INF2-mediated FSGS. Significance Statement The lack of understanding of inverted formin-2 (INF2)-related human diseases has hindered the development of effective therapy. To address the pathological features of protein mistrafficking in both INF2-related neuropathy and FSGS, experiments using in vitro and in vivo models of INF2-related podocytopathy confirmed the hypothesis that INF2 regulates dynein-mediated trafficking of nephrin, and that pathogenic INF2 mutations can disrupt this regulation, resulting in impaired slit diaphragm integrity, proteinuric podocytopathy, and FSGS. Dysregulated dynein-mediated trafficking may be a viable therapeutic target for INF2-related (and perhaps other forms) of FSGS. Visual Abstract