Nephrin is specifically located at the slit diaphragm of glomerular podocytes

TLDR

The Finnish type congenital nephrotic syndrome (NPHS1) is marked by in utero proteinuria and absence of slit diaphragms and foot processes, underscoring the importance of the nephrin gene. This study maps the size and precise location of nephrin, the first protein identified at the podocyte slit diaphragm. The authors propose a zipper‑like model for nephrin assembly at the slit diaphragm, integrating current and prior data. Western blotting detected a 180‑kDa nephrin band in human glomeruli and a 150‑kDa band in transfected cells; immunofluorescence and immunogold labeling localized nephrin to the slit between podocyte foot processes, supporting its essential role in the filtration barrier.

Abstract

We describe here the size and location of nephrin, the first protein to be identified at the glomerular podocyte slit diaphragm. In Western blots, nephrin antibodies generated against the two terminal extracellular Ig domains of recombinant human nephrin recognized a 180-kDa protein in lysates of human glomeruli and a 150-kDa protein in transfected COS-7 cell lysates. In immunofluorescence, antibodies to this transmembrane protein revealed reactivity in the glomerular basement membrane region, whereas the podocyte cell bodies remained negative. In immunogold-stained thin sections, nephrin label was found at the slit between podocyte foot processes. The congenital nephrotic syndrome of the Finnish type (NPHS1), a disease in which the nephrin gene is mutated, is characterized by massive proteinuria already in utero and lack of slit diaphragm and foot processes. These features, together with the now demonstrated localization of nephrin to the slit diaphragm area, suggests an essential role for this protein in the normal glomerular filtration barrier. A zipper-like model for nephrin assembly in the slit diaphragm is discussed, based on the present and previous data.