A novel nanoluciferase transgenic reporter to measure proteinuria in zebrafish

The zebrafish is an important animal system for modelling human diseases. This includes kidney dysfunction as the embryonic kidney (pronephros) shares considerable molecular and morphological homology with the human nephron. Zebrafish also have a high fecundity, with females capable of laying 200-300 eggs per week, thereby facilitating chemical and mutation screening. A key clinical indicator of kidney disease is proteinuria, but a high-throughput readout of proteinuria in the zebrafish is lacking. Coupling the advantages of the zebrafish system with a tool to measure proteinuria will advance the scope for testing the efficacy of drugs to treat kidney diseases. Here, we generated a stable transgenic zebrafish line using the l-fabp10 liver-specific promoter to over-express a nanoluciferase molecule fused with the D3 domain of Receptor-Associated-Protein (RAP) to create NL-D3. In the healthy state, NL-D3 is excreted, but when embryos were treated with chemicals that affected either proximal tubular reabsorption (cisplatin, gentamicin) or glomerular filtration (angiotensin II, Hanks Balanced Salt Solution, Bovine Serum Albumin), NL-D3 presence in the urine increased. Similarly, depletion of several gene products associated with kidney disease (nphs1, nphs2, lrp2a, ocrl, col4a3, col4a4, and col4a5) also induced NL-D3 proteinuria. Furthermore, we found that treating col4a4 depleted zebrafish larvae (a model of Alport syndrome) with captopril reduced proteinuria. Our findings confirm the use of the NL-D3 transgenic zebrafish as a robust and quantifiable proteinuria reporter. Given the feasibility of high-throughput assays in zebrafish, this novel reporter will permit screening for drugs that ameliorate proteinuria and thereby prioritise candidates for further translational studies.