AGRIN IS A MAJOR HEPARAN-SULFATE PROTEOGLYCAN IN THE HUMAN GLOMERULAR-BASEMENT-MEMBRANE

Agrin is a heparan sulfate proteoglycan (HSPG) that is highly concentr ated in the synaptic basal lamina at the neuromuscular junction (NMJ). Agrin-like immunoreactivity is also detected outside the NMJ. Here we show that agrin is a major HSPG component of the human glomerular bas ement membrane (GBM). This is in addition to perlecan, a previously ch aracterized HSPG of basement membranes. Antibodies against agrin and a gainst an unidentified GEM HSPG produced a strong staining of the GEM and the NMJ, different from that observed with anti-perlecan antibodie s. In addition, anti-agrin antisera recognized purified GEM HSPG and c ompeted with an anti-GEM HSPG monoclonal antibody in ELISA. Furthermor e, both antibodies recognized a molecule that migrated in SDS-PAGE as a smear and had a molecular mass of approximately 200-210 kD after deg lycosylation. In immunoelectron microscopy, agrin showed a linear dist ribution along the GBM and was present throughout the width of the CEM . This was again different from perlecan, which was exclusively presen t on the endothelial side of the GEM and was distributed in a nonlinea r manner. Quantitative ELISA showed that, compared with perlecan, the agrin-like GEM HSPG showed a sixfold higher molarity in crude glomerul ar extract. These results show that agrin is a major component of the GEM, indicating that it may play a role in renal ultrafiltration and c ell matrix interaction.