Diminution of Podocyte Anionic Sites in Drug-Induced Proteinuric Rats

Controversial results have been reported about the change in anionic charge density on the glomerular basement membrane (GBM) and podocytes in relation to glomerular protein leakage induced by puromycin aminonucleoside (PAN). So we examined the anionic charge on the glomerular wall of rats with PAN-induced proteinuria. PAN, 15 mg/kg, was intraperitoneally injected daily into female Wistar rats for 4 to 14 days. Examinations performed were as follows: Urinary levels of protein and sialic acid, protein fraction analysis of urine by SDS-PAGE, serum chemistry, cytochemistry for assessment of anionic charge by a cationic poly-L-lysine gold (PLG) method (pH 3.3), digestion tests with neuraminidase and heparitinase, immunocytochemistry for the localization of serum proteins and actin, and conventional light and electron microscopy. In proteinuric rats, the anionic sites on podocytes consisting mainly of sialic acids were decreased from the early stage of protein leakage. The urinary sialic acid level was elevated in advanced proteinuria. The density of anionic sites on the GBM remained mostly unchanged even in severe proteinuria. Serum proteins were identified in dense bodies and vacuoles in the podocytes in proteinuric rats. Disarrangement of actin was seen in flattened foot processes. No detachment of foot processes was observed even in severe proteinuric rats. In conclusion, the decrease in anionic charge density on podocytes is attributable to protein leakage through the glomerulus in PAN-induced proteinuric rats. The anionic charge on GBM and the detachment of foot processes seem to be irrelevant to the primary change leading to protein leakage.