EVIDENCE FOR THE EXISTENCE OF MULTIPLE HEPARAN-SULFATE PROTEOGLYCANS IN THE HUMAN GLOMERULAR-BASEMENT-MEMBRANE AND MESANGIAL MATRIX

Heparan sulfate proteoglycans (HSPGs) are essential components of the glomerular basement membrane (GEM) carrying a strong anionic charge. A well-characterized extracellular HSPG is perlecan, ubiquitously expre ssed in basement membranes. A cDNA construct encoding domains I and II of human perlecan was expressed as a fusion protein with glutathione S-transferase. This fusion protein was used to generate monoclonal ant ibody 95J10. We compared the staining pattern of 95J10 with that of M2 15, a previously prepared mAb that recognizes HSPG isolated from human GEM. In kidney cortex, the antiperlecan mAb 95J10 showed a strong sta ining of the mesangium, Bowman's capsule, the tubular basement membran e, and stained the GEM only slightly, In contrast, M215 predominantly stained the GEM in a linear fashion. Immunoelectron microscopy support ed these results, showing concentrations of perlecan in some regions o f the GEM, whereas the unidentified M215 antigen was homogenously dist ributed throughout the GEM. In other human tissues, both antibodies al so produced a different staining pattern. Furthermore, a polyclonal an tiserum recognizing HSPG isolated from the GEM did not recognize perle can from EHS tumors. These results provide evidence for the presence o f another HSPG in the GEM that is immunologically distinct from perlec an. The absence of perlecan splice variants in the kidney suggests tha t this component is encoded by a different gene than perlecan, Given i ts marked expression in the GEM, this component could be a determining factor in the maintenance of selective glomerular permeability.