Heparan sulfate proteoglycan of murine glomerular basement membrane: relationship between localization of the core protein and localization of fixed negative charges.

Antibodies to a 250,000 molecular weight heparan sulfate proteoglycan (HSPG) core protein purified from PYS-2 cells were prepared in the rabbit. After absorption with laminin, the anti-HSPG serum (AHSPGS) was specific for HSPG by enzyme-linked immunoabsorbent assay (ELISA). Immunoelectron microscopy showed that AHSPGS reacted with the mouse glomerular basement membrane (GBM) or, more precisely, with three HSPG rich layers, i.e., (i) the lamina rara interna in a discrete or interrupted-linear pattern, (ii) the interface between the GBM and the soles of the foot processes, and (iii) the lamina rara externa in a finely discrete pattern. The localization of HSPG in the GBM was very similar to that of the fixed negative charges detected with polyethyleneimine (PEI). When mice were treated with heparitinase, binding of PEI was seen only on the cell surface including the foot process soles (ii) but not in the GBM (i and iii), while the localization of HSPG core protein was unaltered. These results suggest that the localization of the HSPG core protein was correlated with that of the fixed negative charges in the GBM (i and iii). The foot process base (ii) seems to be a complicated zone since the PEI binding in this area was less affected by heparitinase treatment, while this area has been reported to have a lower sialic acid content than the foot process surface facing the urinary space.