PODOCYTIC CYTOSKELETAL DISAGGREGATION AND BASEMENT-MEMBRANE DETACHMENT IN PUROMYCIN AMINONUCLEOSIDE NEPHROSIS

Puromycin aminonucleoside-(PAN) treated rats develop acute nephrotic s yndrome, mimicking human minimal lesion disease. In PAN nephrosis, pod ocyte detachment from the glomerular basement membrane (GBM) is the mo st likely cause of massive proteinuria in this model. To elucidate fur ther the mechanism of PAN-induced cellular dysfunction, new methods we re employed to visualize podocyte cytoskeletal aggregation and to meas ure fibrillar attachment to the GBM. Adult Sprague-Dawley rats (n = 41 group) received a single tail-vein injection of PAN (75 mg/kg). On da ys 1, 2, 3, and 5 following injection, 24-hour urine collections were obtained for creatinine clearance, albuminuria, and total proteinuria. Then kidneys from each group were fixed by perfusion. Podocytic cytos keleton was visualized by scanning electron microscopy. Subepithelial GBM staining and attachment fiber number, observed on digitized images of transmission electron micrograpbs, were quantitated with computer- based density analysis. A significant reduction in attachment fiber nu mber in the GBM lamina rara externa occurred by day 5. on scanning ele ctron micrographs, the secondary and tertiary podocytic processes were observed to be formed by highly aggregated cytoskeleton, which became partially disaggregated by day 3, was totally absent by day 5, and no rmalized by day 20. Immunogold staining revealed that actin and vincul in localized to the tertiary podocytic processes in the normal state w ere dispersed into the cell body following PAN. Podocyte cytoskeletal disaggregation precedes, and detachment from the GBM occurs simultaneo usly with, the onset of massive proteinuria in the PAN model.