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 expressed 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 antibody 95J10. We compared the staining pattern of 95J10 with that of M215, a previously prepared mAb that recognizes HSPG isolated from human GEM. In kidney cortex, the antiperlecan mAb 95J10 showed a strong staining of the mesangium, Bowman's capsule, the tubular basement membrane, and stained the GEM only slightly, In contrast, M215 predominantly stained the GEM in a linear fashion. Immunoelectron microscopy supported these results, showing concentrations of perlecan in some regions of the GEM, whereas the unidentified M215 antigen was homogenously distributed throughout the GEM. In other human tissues, both antibodies also produced a different staining pattern. Furthermore, a polyclonal antiserum recognizing HSPG isolated from the GEM did not recognize perlecan from EHS tumors. These results provide evidence for the presence of another HSPG in the GEM that is immunologically distinct from perlecan. The absence of perlecan splice variants in the kidney suggests that this component is encoded by a different gene than perlecan, Given its marked expression in the GEM, this component could be a determining factor in the maintenance of selective glomerular permeability.