Nephrin Localizes at the Podocyte Filtration Slit Area and Is Characteristically Spliced in the Human Kidney

Abstract

Morphological and functional evidence suggests that the glomerular visceral epithelial cells, podocytes, are crucial for maintaining the glomerular permeability barrier. 1-3Podocytes attach to the underlying basement membrane by mechanisms involving matrix receptors capable of inside-out and outside-in signaling that is important for rapid cell shape changes. 4,5 The attachment via integrins also appears crucial for the filtration function as evidenced by recent data for mice with genetic disruption especially of ␣3␤1 integrin. 6 The distinct structure of podocytes with primary and secondary foot processes interlinked by filtration slits appears to provide additional means for dynamic shape changes and regulation of functions. The composition and exact role of the filtration slits, however, remain to be determined. The structural complexity of podocytes is the characteristic feature of an intact glomerular filtration barrier, as contrasted with the flattening, retraction, and fusion of foot processes in human and experimental diseases with proteinuria.

Nephrin Forms a Complex with Adherens Junction Proteins and CASK in Podocytes and in Madin-Darby Canine Kidney Cells Expressing Nephrin

“…Thus the distribution of nephrin in MDCK cells resembles that in the glomerulus where nephrin has been localized in both the junctional or slit diaphragm region and at the apical domain of podocytes. [3][4][5] …”

“…As already mentioned, in podocytes nephrin was found both at the slit diaphragm and along the apical plasma membrane. [3][4][5] …”

“…1 NPHS1 encodes for nephrin, 1 a member of the immunoglobulin (Ig) superfamily of cell adhesion molecules, 2 which is localized in the glomerular slit diaphragm and has been suggested to form the framework of this specialized cell adhesion structure. [3][4][5] Slit diaphragms are important components of the glomerular filtration barrier. They bridge the urinary spaces between the foot processes of the glomerular epithelium and serve to attach foot processes to one another.…”

A 100-kDa urinary protein is associated with insulin resistance in offspring of type 2 diabetic patients

“…We have previously shown that an alternatively spliced nephrin, nephrin α, exists in the human glomerulus at the mRNA level [22]. It is possible that the 100-kDa protein represents this form both in glomeruli and urine.…”

“…Normal kidney tissue was obtained from cadaver kidneys taken for transplantation but not grafted because of vascular anatomical abnormalities (Department of Surgery, Helsinki University Central Hospital, Finland) in accordance with the principles of the Declaration of Helsinki. Glomeruli were isolated as described earlier [22], followed by extraction of membrane proteins using RIPA buffer (150 mmol/l NaCl, 1% v/v NP-40, 0.5% w/v Na-deoxycholate, 0.1% w/v SDS and 50 mmol/l Tris, pH 8.0) with Complete Miniprotease inhibitor cocktail (Roche Diagnostics, Mannheim, Germany).…”