In situ evaluation of podocin in normal and glomerular diseases

BACKGROUND: Mutations of the NPHS2 gene are responsible for autosomal-recessive steroid-resistant nephrotic syndrome. Its product, podocin, faces the slit diaphragm area with its two ends in the cytoplasm of foot processes. METHODS: We generated rabbit polyclonal antibodies against conjugated peptides from human podocin N- and C-termini, and studied podocin and synaptopodin using kidney tissues of normal humans and those with glomerular diseases. RESULTS: Antipodocin antibodies detected the original 42 kD fragment and an extra smaller fragment by Western blot analysis using human isolated mature glomeruli. RNA analysis showed two bands, the original and the other of a decreased length. Immunohistochemically, podocin was detected in a linear pattern along the glomerular capillary loop. Antipodocin antibody (C-terminal) stained the smooth muscles of renal arterioles and aorta. Among 42 patients, podocin was normally expressed in glomeruli in purpura nephritis, IgA nephropathy (IgAN), and minimal-change disease (MCD), while it was either decreased or absent in most subjects with focal segmental glomerulosclerosis (FSGS). The expression of synaptopodin was similar to that of podocin, although some discrepancy existed. CONCLUSION: Although indirect, our data suggest the existence of a vascular isoform of podocin with a different molecular mass. We propose that examination of podocin expression may help differentiate MCD from FSGS.