[Structure and function of the glomerular filtration barrier]

The aim of the review is to discuss recent investigations on the glomerular filtration barrier. The barrier consists of three layers: the vascular endothelium, the glomerular basement membrane and the slit diaphragm located between podocyte foot processes. The main components of the slit diaphragm are nephrin, the product of NPHS1 gene and podocin, the product of NPHS2 gene. Mutations in NPHS1 lead to congenital nephrotic syndrome of the Finnish type (CNF), whereas NPHS2 mutations result in focal segmental glomerulosclerosis (FSGS). In both cases massive proteinuria is accompanied by the effacement of podocyte foot processess. Reduced expression and redistribution of nephrin and podocin are also seen in podocytes of patients with acquired glomerulopathies. The results suggest that those proteins play a pivotal role in the processes responsible for glomerular filtration. Together with podocin and CD2AP (CD2-associated protein), nephrin forms a complex determining the integrity of the slit diaphragm. Its function has not yet been fully understood and the pathways of signal transduction need to be elucidated.