Modeling Monogenic Human Nephrotic Syndrome in the <i>Drosophila</i> Garland Cell Nephrocyte.

Abstract

Steroid-resistant nephrotic syndrome is characterized by podocyte dysfunction. <i>Drosophila</i> garland cell nephrocytes are podocyte-like cells and thus provide a potential <i>in vivo</i> 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 <i>Drosophila</i> 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 <i>Drosophila</i> 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 <i>Coq2</i>, the silencing of which disrupted slit diaphragm morphology. Restoration of CoQ₁₀ synthesis by vanillic acid partially rescued the phenotypic and functional alterations induced by <i>Coq2</i>-RNAi. Notably, <i>Coq2</i> colocalized with mitochondria, and <i>Coq2</i> silencing increased the formation of reactive oxygen species (ROS). Silencing of <i>ND75</i>, a subunit of the mitochondrial respiratory chain that controls ROS formation independently of CoQ₁₀, phenocopied the effect of <i>Coq2</i>-RNAi. Moreover, the ROS scavenger glutathione partially rescued the effects of <i>Coq2</i>-RNAi. In conclusion, <i>Drosophila</i> garland cell nephrocytes provide a model with which to study the pathogenesis of nephrotic syndrome, and ROS formation may be a pathomechanism of <i>COQ2</i>-nephropathy.