Simultaneous assessment of glomerular filtration and barrier function in live zebrafish

The zebrafish pronephros is a well-established model to study glomerular development, structure, and function. A few methods have been described to evaluate glomerular barrier function in zebrafish larvae so far. However, there is a need to assess glomerular filtration as well. In the present study, we extended the available methods by simultaneously measuring the intravascular clearances of Alexa fluor 647-conjugated 10-kDa dextran and FITC-conjugated 500-kDa dextran as indicators of glomerular filtration and barrier function, respectively. After intravascular injection of the dextrans, mean fluorescence intensities of both dextrans were measured in the cardinal vein of living zebrafish (4 days postfertilization) by confocal microscopy over time. We demonstrated that injected 10-kDa dextran was rapidly cleared from the circulation, became visible in the lumen of the pronephric tubule, quickly accumulated in tubular cells, and was detectably excreted at the cloaca. In contrast, 500-kDa dextran could not be visualized in the tubule at any time point. To check whether alterations in glomerular function can be quantified by our method, we injected morpholino oligonucleotides (MOs) against zebrafish nonmuscle myosin heavy chain IIA (zMyh9) or apolipoprotein L1 (zApol1). While glomerular filtration was reduced in zebrafish nonmuscle myosin heavy chain IIA MO-injected larvae, glomerular barrier function remained intact. In contrast, in zebrafish apolipoprotein L1 MO-injected larvae, glomerular barrier function was compromised as 500-kDa dextran disappeared from the circulation and became visible in tubular cells. In summary, we present a novel method that allows to simultaneously assess glomerular filtration and barrier function in live zebrafish.