title: New perspectives on the renal slit diaphragm protein podocin.
abstract: Podocin is a critical component of the glomerular filtration barrier, its mutations causing recessive steroid-resistant nephrotic syndrome. A GenBank analysis of the human podocin (NPHS2) gene resulted in the possible existence of a new splice variant of podocin in the kidney, missing the in-frame of exon 5, encoding the prohibitin homology domain. Using RT-polymerase chain reaction and immunoblotting followed by sequence analysis, we are for the first time able to prove the expression of a novel podocin isoform (isoform 2), exclusively and constitutively expressed in human podocytes. Furthermore, we reveal singular extrarenal podocin expression in human and murine testis. Our data show the Sertoli cells of the seminiferous tubules to be the origin of testicular podocin. Confocal laser microscopy illustrates the co-localization of podocin with filamentous actin within Sertoli cells, suggesting a role of podocin in the blood/testis barrier. These results led to the rationale to examine podocin expression in testes of men with Sertoli cell-only syndrome, a disorder characterized by azoospermia. Interestingly, we observed a complete down-regulation of podocin mRNA in Sertoli cell-only syndrome, indicating a possible role of podocin in the pathogenesis of this germinal aplasia. Men with Sertoli cell-only syndrome show normal renal podocin expression, suggesting an alternate regulation of the testicular promoter. Our findings may change the perception of podocin and give new insights into the ultrastructure of glomerular slit diaphragm and the blood/testis barrier.
authors.affiliation: Department of Medicine, Johannes Gutenberg University, Mainz, Germany. relle@uni-mainz.de
authors.forename: Manfred
authors.initials: M
authors.lastname: Relle
authors.forename: Hannes
authors.initials: H
authors.lastname: Cash
authors.forename: Christoph
authors.initials: C
authors.lastname: Brochhausen
authors.forename: Dennis
authors.initials: D
authors.lastname: Strand
authors.forename: Julia
authors.initials: J
authors.lastname: Menke
authors.forename: Peter R
authors.initials: PR
authors.lastname: Galle
authors.forename: Andreas
authors.initials: A
authors.lastname: Schwarting
mesh_terms: D000328:Adult; D000368:Aged; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D020869:Gene Expression Profiling; D006801:Humans; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics*; D051379:Mice; D018613:Microscopy, Confocal; D008875:Middle Aged; D008969:Molecular Sequence Data; D050199:Podocytes / Q000378:metabolism*; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D054331:Sertoli Cell-Only Syndrome / Q000378:metabolism*; D012708:Sertoli Cells / Q000378:metabolism*; D055815:Young Adult
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C407223:NPHS2 protein; D020033:Protein Isoforms