The glomerular filtration barrier is composed of endothelial cells, basement membrane, and podocytes.
The glomerular basement membrane is composed of a multitude of proteins, including collagen IV, heparan sulfate proteoglycans, and laminin, among others.
The slit diaphragm, which is seen as a membrane covering the space between adjacent foot processes close to the basement membrane, is an extremely important structure with a crucial role in permselectivity of the filtration barrier. Its composition is now understood to consist primarily of a unique protein called nephrin.
Mutations in the gene-encoding nephrin are known to result in the Finnish type of nephrotic syndrome. The exact mechanism by which nephrin controls permselectivity is not yet clear, but it is known to interact with several podocyte proteins including CD2AP, podocin, and alpha-actinin-4.
Abnormalities of any of these proteins may result in proteinuria.
See also
nephrin
common acquired glomerulopathies
podocytes
transcription factors (WT1, PAX2)
References
Tryggvason K, Patrakka J, Wartiovaara J. Hereditary proteinuria syndromes and mechanisms of proteinuria. N Engl J Med. 2006 Mar 30;354(13):1387-401. PMID: 16571882
Akhtar M, Al Mana H. Molecular basis of proteinuria. Adv Anat Pathol. 2004 Nov;11(6):304-9. PMID: 15505531