Background: We recently reported that nephrin, a major slit-diaphragm protein, is phosphorylated at Y1204 and Y1228 in normal human glomeruli and that phosphorylation decreased significantly in minimal-change nephrosis. These results indicate that phosphorylation of nephrin is important for maintenance of normal podocyte morphology and function. On the other hand, phosphorylation of nephrin was reportedly increased in certain animal models of glomerular injury.

Methods: We performed immunofluorescent and immunoelectron staining of phosphorylated nephrin in human kidney biopsy specimens of membranous nephropathy (MN) to investigate whether phosphorylation of nephrin was altered in human MN and whether it correlated with MN staging.

Results: Although aberrant localization of phosphorylated nephrin was detected using immunoelectron microscopy in stage I MN, a decrease in the immunofluorescent intensity of phosphorylated nephrin was not observed in stage I, and only a slight decrease was seen in stages II, III, and IV compared with controls. No significant correlation between nephrin phosphorylation and proteinuria was observed.

Conclusions: Nephrin phosphorylation was not significantly decreased in the early stage of MN.