Modeling Monogenic Human Nephrotic Syndrome in the Drosophila Garland Cell Nephrocyte

Steroid-resistant nephrotic syndrome is characterized by podocyte dysfunction. Drosophila garland cell nephrocytes are podocyte-like cells and thus provide a potential in vivo model in which to study the pathogenesis of nephrotic syndrome. However, relevant pathomechanisms of nephrotic syndrome have not been studied in nephrocytes. Here, we discovered that two Drosophila slit diaphragm proteins, orthologs of the human genes encoding nephrin and nephrin-like protein 1, colocalize within a fingerprint-like staining pattern that correlates with ultrastructural morphology. Using RNAi and conditional CRISPR/Cas9 in nephrocytes, we found this pattern depends on the expression of both orthologs. Tracer endocytosis by nephrocytes required Cubilin and reflected size selectivity analogous to that of glomerular function. Using RNAi and tracer endocytosis as a functional read-out, we screened Drosophila orthologs of human monogenic causes of nephrotic syndrome and observed conservation of the central pathogenetic alterations. We focused on the coenzyme Q₁₀ (CoQ₁₀) biosynthesis gene Coq2, the silencing of which disrupted slit diaphragm morphology. Restoration of CoQ₁₀ synthesis by vanillic acid partially rescued the phenotypic and functional alterations induced by Coq2-RNAi. Notably, Coq2 colocalized with mitochondria, and Coq2 silencing increased the formation of reactive oxygen species (ROS). Silencing of ND75, a subunit of the mitochondrial respiratory chain that controls ROS formation independently of CoQ₁₀, phenocopied the effect of Coq2-RNAi. Moreover, the ROS scavenger glutathione partially rescued the effects of Coq2-RNAi. In conclusion, Drosophila garland cell nephrocytes provide a model with which to study the pathogenesis of nephrotic syndrome, and ROS formation may be a pathomechanism of COQ2-nephropathy.