Nephrin and podocin dissociate at the onset of proteinuria in experimental membranous nephropathy.
BACKGROUND
The slit diaphragm plays a critical role in maintaining the barrier function of the glomerular capillary wall. The pathogenic mechanism of proteinuria in membranous nephropathy remains uncertain. This study was undertaken to analyze the pathogenic role of slit diaphragm in proteinuria in experimental membranous nephropathy.


METHODS
The expression and the localization of slit diaphragm-associated molecules (nephrin, podocin, and CD2AP) and other podocyte-associated molecules (podocalyxin and alpha(3) integrin) in passive and active Heymann nephritis were analyzed by immunofluorescence and Western blot analysis. The interaction of slit diaphragm-associated molecules was investigated by the dual-labeling immunofluorescence method. The mRNA expression of these molecules was also analyzed.


RESULTS
Shifts in nephrin and podocin staining patterns, from linear to granular, were detected in the early stages of passive Heymann nephritis. These shifts were not parallel, and the dissociation of these molecules was detected by the dual-labeling immunofluorescence method in passive and active Heymann nephritis. Western blot analyses with sequentially solubilized materials indicated that the nephrin-rich fraction changed from being partly detergent-resistant to being predominantly detergent-soluble. This change did not occur with podocin. Nephrin excreted into urine was already detected in the early stages of passive Heymann nephritis. Decreased mRNA expression of nephrin and podocin was observed before the onset of proteinuria. By contrast, no extensive change in the expression of alpha(3) integrin was observed in this study.


CONCLUSIONS
Nephrin is dissociated from podocin and excreted into urine in the early stages of Heymann nephritis. The reduced expression of nephrin and podocin, along with their dissociation, may contribute to the development of proteinuria in Heymann nephritis.
Nakatsue
Takeshi
T
Department of Cell Biology, Institute of Nephrology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.
Koike
Hiroko
H
Han
Gi Dong
GD
Suzuki
Koichi
K
Miyauchi
Naoko
N
Yuan
Huaiping
H
Salant
David J
DJ
Gejyo
Fumitake
F
Shimizu
Fujio
F
Kawachi
Hiroshi
H
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D003598:Cytoskeletal Proteins; D005260:Female; D005455:Fluorescent Antibody Technique; D015433:Glomerulonephritis, Membranous / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008565:Membrane Proteins / Q000032:analysis* / Q000235:genetics; D008969:Molecular Sequence Data; D011506:Proteins / Q000032:analysis; D011507:Proteinuria / Q000209:etiology / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D011917:Rats, Inbred Lew; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D012756:Sheep
D048868:Adaptor Proteins, Signal Transducing; C114545:CD2-associated protein; D003598:Cytoskeletal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C407223:NPHS2 protein; D011506:Proteins; C113267:nephrin