A method to facilitate and monitor expression of exogenous genes in the rat kidney using plasmid and viral vectors

Gene therapy has been proposed as a novel alternative to treat kidney disease. This goal has been hindered by the inability to reliably deliver transgenes to target cells throughout the kidney, while minimizing injury. Since hydrodynamic forces have previously shown promising results, we optimized this approach and designed a method that utilizes retrograde renal vein injections to facilitate transgene expression in rat kidneys. We show, using intravital fluorescence two-photon microscopy, that fluorescent albumin and dextrans injected into the renal vein under defined conditions of hydrodynamic pressure distribute broadly throughout the kidney in live animals. We found injection parameters that result in no kidney injury as determined by intravital microscopy, histology, and serum creatinine measurements. Plasmids, baculovirus, and adenovirus vectors, designed to express EGFP, EGFP-actin, EGFP-occludin, EGFP-tubulin, tdTomato-H2B, or RFP-actin fusion proteins, were introduced into live kidneys in a similar fashion. Gene expression was then observed in live and ex vivo kidneys using two-photon imaging and confocal laser scanning microscopy. We recorded widespread fluorescent protein expression lasting more than 1 mo after introduction of transgenes. Plasmid and adenovirus vectors provided gene transfer efficiencies ranging from 50 to 90%, compared with 10-50% using baculovirus. Using plas-mids and adenovirus, fluorescent protein expression was observed 1) in proximal and distal tubule epithelial cells; 2) within glomeruli; and 3) within the peritubular interstitium. In isolated kidneys, fluorescent protein expression was observed from the cortex to the papilla. These results provide a robust approach for gene delivery and the study of protein function in live mammal kidneys.