Nephrin in experimental glomerular disease

Background The recently identified gene NPHS1 with its mutations causing co ngenital nephrotic syndrome of the Finnish type (CNF) is highly promising i n providing new understanding of pathophysiology of proteinuria. Earlier we cloned a rat NPHS1 homologue, as well as characterized and raised antibodi es to the respective protein product nephrin. Methods. Changes in the expression levels of nephrin-specific mRNA in commo nly used experimental models of proteinuria were examined using semiquantit ative reverse transcription-polymerase chain reaction, immunofluorescence, and immunoelectron microscopy (IEM) of nephrin. Results. Notably, a 40% down-regulation of the nephrin-specific mRNA of cor tical kidney was seen already at day 3 after induction of the puromycin ami nonucleoside nephrosis (PAN), while no major elevation of urinary protein s ecretion was seen at this stage. A further decrease of 80% of nephrin messa ge was seen at the peak of proteinuria at day 10. A similar decrease of up to 70% from the basal levels was seen in mercuric chloride-treated rats. Ch anges in the protein expression paralleled those of the mRNA in indirect im munofluorescence. Interestingly, a remarkable plasmalemmal dislocation from the normal expression site at the interpodocyte filtration slits could be observed in IEM. Conclusions. Nephrin appears to be an important causative molecule of prote inuria and shows a remarkable redistribution from the filtration slits to t he podocyte plasma membrane, especially in PAN.