Transgenic zebrafish modeling low-molecular-weight proteinuria and lysosomal storage diseases

Abstract

Epithelial cells lining the proximal tubule of the kidneyreabsorb and metabolize most of thefiltered low-molecular-weight proteins through receptor-mediatedendocytosis and lysosomal processing. Congenital andacquired dysfunctions of the proximal tubule areconsistently reflected by the inappropriate loss of solutesincluding low-molecular-weight proteins in the urine. Thezebrafish pronephros shares individual functionalsegments with the human nephron, including lrp2a/megalin-dependent endocytic transport processes of theproximal tubule. Although the zebrafish has been used as amodel organism for toxicological studies and drugdiscovery, there is no available assay that allows large-scaleassessment of proximal tubule function in larval or adultstages. Here we establish a transgenicTg(lfabp::1/2vdbp-mCherry)zebrafish line expressing in the liver the N-terminal region of vitamin D-binding protein coupled tothe acid-insensitive, red monomericfluorescent proteinmCherry (1/2vdbp-mCherry). This low-molecular-weightprotein construct is secreted into the bloodstream,filteredthrough the glomerulus, reabsorbed by receptor-mediatedendocytosis and processed in the lysosomes of proximaltubule cells of thefish. Thus, our proof-of-concept studiesusing zebrafish larvae knockout forlrp2aandclcn7orexposed to known nephrotoxins (gentamicin and cisplatin)demonstrate that this transgenic line is useful to monitorlow-molecular-weight proteinuria and lysosomalprocessing. This represents a powerful new modelorganism for drug screening and studies of nephrotoxicity.