Foothold of NPHS2 mutations in primary nephrotic syndrome

Glomerular podocytes are highly specialized cells with a complex cytoarchitecture. Their most prominent features are interdigitated foot processes with filtration slits in between. These are bridged by the slit diaphragm, which plays a major role in establishing the selective permeability of the glomerular filtration barrier. We searched Medline and Pubmed using the combination of keywords "NPHS2", "podocin", "steroid-resistant nephrotic syndrome," and "genetics" to identify studies describing an association between NPHS2 gene and renal disease. The highly dynamic foot processes contain an actin-based contractile apparatus comparable to that of smooth muscle cells. Mutations affecting several podocyte proteins lead to rearrangement of the cytoskeleton, disruption of the filtration barrier, and subsequent renal disease. The fact that the dynamic regulation of the podocyte cytoskeleton is vital to kidney function has led to podocytes emerging as an excellent model system for studying actin cytoskeleton dynamics in a physiological context. Injury to podocytes leads to proteinuria, a hallmark of most glomerular diseases. Recent studies have led to a considerable increase in our understanding of podocyte biology including composition and arrangement of the cytoskeleton involved in the control of ultrafiltration. Moreover, disturbances of podocyte architecture resulting in the retraction of foot processes and proteinuria appear to be a common theme in the progression of an acquired glomerular disease. In hereditary nephrotic syndromes identified over the last few years, all mutated gene products were localized in podocytes. This review integrates our recent physiological and molecular understanding of the role of podocytes during the maintenance and failure of the glomerular filtration barrier.