Nephrin strands contribute to a porous slit diaphragm scaffold as revealed by electron tomography.

Abstract

Nephrin is a key functional component of the slit diaphragm, the structurally unresolved molecular filter in renal glomerular capillaries. Abnormal nephrin or its absence results in severe proteinuria and loss of the slit diaphragm. The diaphragm is a thin extracellular membrane spanning the approximately 40-nm-wide filtration slit between podocyte foot processes covering the capillary surface. Using electron tomography, we show that the slit diaphragm comprises a network of winding molecular strands with pores the same size as or smaller than albumin molecules, as demonstrated in humans, rats, and mice. In the network, which is occasionally stratified, immunogold-nephrin antibodies labeled individually detectable globular cross strands, about 35 nm in length, lining the lateral elongated pores. The cross strands, emanating from both sides of the slit, contacted at the slit center but had free distal endings. Shorter strands associated with the cross strands were observed at their base. Immunolabeling of recombinant nephrin molecules on transfected cells and in vitrified solution corroborated the findings in kidney. Nephrin-deficient proteinuric patients with Finnish-type congenital nephrosis and nephrin-knockout mice had only narrow filtration slits that lacked the slit diaphragm network and the 35-nm-long strands but contained shorter molecular structures. The results suggest the direct involvement of nephrin molecules in constituting the macromolecule-retaining slit diaphragm and its pores.

• Authors: Jorma Wartiovaara, Lars-Göran Ofverstedt, Jamshid Khoshnoodi, Jingjing Zhang, Eetu Mäkelä, Sara Sandin, Vesa Ruotsalainen, R Holland Cheng, Hannu Jalanko, Ulf Skoglund, Karl Tryggvason
• Journal: The Journal of clinical investigation (J Clin Invest) Vol. 114 Issue 10 Pg. 1475-83 (Nov 2004) ISSN: 0021-9738 [Print] United States
• PMID: 15545998 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Disulfides
• Immunoglobulin G
• Membrane Proteins
• Proteins
• Recombinant Proteins
• nephrin

Topics

• Animals
• Capillaries (chemistry, diagnostic imaging, ultrastructure)
• Cell Line
• Disulfides (chemistry)
• Genetic Variation
• Humans
• Immunoglobulin G (chemistry)
• Immunohistochemistry
• Kidney Glomerulus (blood supply, diagnostic imaging, ultrastructure)
• Membrane Proteins
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Protein Structure, Tertiary
• Proteins (chemistry, genetics, metabolism, ultrastructure)
• Rats
• Rats, Sprague-Dawley
• Recombinant Proteins (chemistry, metabolism, ultrastructure)
• Ultrasonography